1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly, it relates to a semiconductor device having an IGBT (Insulated Gate Bipolar Transistor).
2. Description of the Background Art
An IGBT has both of high withstand voltage/high current characteristics of a bipolar transistor and high frequency characteristics of a MOSFET (Metal Oxide Semiconductor Field-Effect Transistor). An IGBT having the so-called LPT (Light Punch Through) structure (Field-STOP structure) including a buffer region provided between a drift region and a collector region is known as such an IGBT (refer to Japanese Patent Laying-Open Nos. 2004-311481, 2001-332729, 10-050724 (1998), 2007-019518, 2004-103982 and 2003-338626).
However, conventional IGBTs having the LPT structure include such an IGBT that the resistance of a safe operating area upon cutoff of a short-circuit current, i.e., the so-called SCSOA (Short Circuit Safe Operation Area) tends to be low and such an IGBT that the margin of the SCSOA resistance tends to be excessive, and it is difficult to ensure a proper margin.